Is there an easy method to do an on the fly conversion of a standard epoch time (seconds from 1970) to more readable date format?

Does Unix have anything built in to do this?

Look at datecalc. That should have what you are looking for.

You can do this as well. But I doubt it will be supported in all versions of linux.

date -d '1970-01-01 UTC 1126884183 seconds' +"%Y-%m-%d %T %z"

2005-09-16 08:23:03 -0700

Each version of unix handles timezones a little differently. Ignoring timezones more or less, this comes fairly close

#! /usr/bin/ksh


#
#  convert unix time to a string
#
#   time="$(unixsecond2timestring $seconds)" is
#      similiar to the c construct:
#               strcpy(time,ctime(&xdate));
#      except that it ignores timezone considerations.
#      This means that it is exactly like:
#          strcpy(time,asctime(gmtime(&xdate)));
#
#      The only way to handle timezones is to figure out
#      your local number of seconds difference from GMT and
#      adjust the value of seconds before passing it.  This
#      means that for small values of "seconds" you may adjust
#      it to a negative number.  That's ok, this routine can
#      handle numbers in the range -86400 to 2147483647.
#
unixsecond2timestring() {
        integer uxsec mjd daysecond hour hoursecond minute second
        typeset -Z2 val
        typeset -R2 val2
        typeset -L3 fdow
        typeset dow time year month day
        typeset months
        set -A months xxx Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec
        uxsec=$1

#
#  Calculate
#    mjd=modified julian day number  (range is 40586 - 65442)
#      Dec 31, 1969 has  mjd=40586
#      Jan 19, 2038 has  mjd=65442
#    daysecond=number of second during the day (range is 0 - 86399)
#    hoursecond=number of second during hour   (range is 0 - 3599)
#    hour, minute, second represent current time
#
        ((mjd=(uxsec/86400)+40587))
        ((daysecond=uxsec%86400))
        ((hour=daysecond/3600))
        ((hoursecond=daysecond-(hour*3600)))
        ((minute=hoursecond/60))
        ((second=hoursecond%60))

#
#    Adjust things if we are negative
        if ((uxsec<0)) ; then
                ((mjd=mjd-1))
                ((hour=(hour+24)%24))
        fi

#
#    Convert mjd to year, month day and get dow (day of week)
        datecalc -j $mjd | read year month day
        dow=$(datecalc -D $year $month $day)

#
#    Format the date
        val=$hour
        time="${val}:"
        val=$minute
        time="${time}${val}:"
        val=$second
        time="${time}${val} $year"
        fdow=$dow
        val2=$day
        time="${fdow} ${months[month]} $val2 $time"
        echo "$time"
        return
}


integer unixsecond
typeset -R11 dsecond

while (($#)) ; do
        unixsecond=$1
        shift
        time1=$(unixsecond2timestring $unixsecond)
        dsecond=$unixsecond
        ((unixsecond2=unixsecond-(5*3600)))
        time2=$(unixsecond2timestring $unixsecond2)

        print "arg = $dsecond     ${time1}    ${time2}"
done
exit 0

ruby -e 'puts Time.at(1126884183).strftime("%Y-%m-%d")'

2005-09-16

gawk 'BEGIN{print strftime("%Y-%m-%d",1126884183)}'